Syntax Magazine

SYNTAX :

se & SERVING —
Tye: TiMex-SINCLAIR FAMILY

r. PERSONAL COMPUTERS

A PUBLICATION OF THE HARVARD GROUP

VOL ..3' NOi7

IN THIS ISSUE

4K Programs
Pie Tae -TOG..+ vss 2d see 6
8K Programs
Fbying Birra. .sacsee seed
Grandson of Big
Characters...««e<seeeL7
Household Finances....4
Improved Data Input..18
Beginners' BASIC
More: On INKBYS <<.< <2 e003
Beginners' Machine Code

PUSHing and POPping..15.

Classified Ads.........21
Déar. EGLCOf.i<%ss we'wana 2
Hardware Project

4K-8K ROM Switch......8
Hardware Review

CAI/O Board and

PEINCELs +. cas ceaeesecel
Machine Language

Keyboard Scanning.....6
News, New Products..1,2,3
Numbers Held Inexactly.14
Program Improvements...21
Subscription InfO.s.:0.623
Users” Groups. <6sscsesad

Index of Advertisers

Byte-Back..cccccccccsee ed
LJH Enterprises........18
Memotech Corp.......eeee19
Microcomputers Plus.....9
Mindware, Inc.......10,11
Sinclair Research......./7
S SS. COs seu Speier sees
SO€ftsync; INGssksaedess 63
Zeta Software...eee..eeel4

Subscribers: Remember to
return your white renewal
card early to get a free
SYNTAX binder.

ISSN 0273-2696 JUL, 1982

TIMEX TO RETAIL TS1000 PRODUCTS IN JULY

Although not specific, Timex Computer
Corporation plans to have TS1000 products in
some "major department and discount stores"
by late July according to a Timex spokes-
person. Timex has 14 software packages,
ranging $9.95 to $19.95, in addition to
$99.95 TS1000 computers and $49.95 16K RAMs.

TS1000 service will be in Timex' Little
Rock, AR, repair facility; current 2ZX80/81
owners should still send their machines to
Microsync for in-warranty service. No
details yet on an 800 number support line.

MINDWARE INTRODUCES ZX-TS1000 PRINTER

At the recent Consumer Electronics Show
in Chicago, Mindware, Inc. revealed their new
MW 100 printer. The 16-column, 5x7 dot-
matrix printer works with 8K ZX computers and
TS1000s, using disposable endless-loop ribbon
(blue or black) and 1 3/4" plain paper tape
from office supply stores.

You need no interface or extra power
supply; the MW100 plugs directly on the rear
edge connector and extends the buss for your
use. Using keyboard commands LLIST, LPRINT
and COPY, the MW printer operates in 3 modes:
wraparound, 16 column truncated, and split

screen. Split screen dumps the left half of
a screen, then the right half, to the
printer. Print speed is 16 cps.

According to Mike Levy of Mindware,
shipments will start in late July. Price:
about $120. (Watch SYNTAX for an early
review.) Mindware, Inc., 70 Boston Post
Road, Wayland, MA 01778, 617/358-7175.

NATIONAL ELECTRONICS III CLOSES SHOP

National Electronics III of Concord, TN,
is no longer in operation. They formerly
repaired out-of-warranty ZX80/8ls, as
reported in SYNTAX, Feb.82.

NEW PRODUCTS AND SERVICES

Exclusively for users in the LA-MS
area: Nonauthorized out-of-warranty
service on ZX81 kits. brice:
$8.50/hr (1 hr. min.) plus parts.
Tracy Norris says turnaround runs
48 hours. Send your computer with
a detailed description of the prob-
lem; they will write or call col-
lect with an estimate. Norris
Radio and Electronics, 144 Terry
Dr., Slidell, LA 70458.

ZX80/81 Users' Library will run a
user-generated program library.
Subscription service will sell pro-
grams ($1.50 for 1K, $3 for 16K) to
members and trade two free programs
for accepted submissions. A news-
letter will be published periodic-—
ally, according to a Users' Library
release. Yearly subscription $25
in US, $32 outside US. New sub-
scribers before 7/31/82 get 15
months for the year price. 2ZX80/81
Users' Library, Suite 434, 4614
Kilauea Ave., Honolulu, HI 96816.

You can now buy the 2X99 automatic
tape controller in the US. You get
software control of up to 4 tape
recorders using a 2K ROM containing
the tape operating system, accessed
by USR calls. It also has a built-
in RS 232 printer interface and
ASCII converter so you can hook any
serial printer to an 8K computer.
Price: $150. Also availble, a
cased big keyboard with repeat key
for $75 and game and application
software under $20. Data-assette,
52 Ss 3rd St., Oxford, PA 19363,
215/932-3626.

Cheap 16K memory for ZX81s costs
only £19.95 (about $34.90). It
uses NMOS 4116 dynamic RAM chips
and runs on the computer's power
supply. According to EconoTech, it
has snug-fitting gold-plated con-
tacts, is fully compatible with ZX
printers and comes with a 6-month
guarantee. EconoTech, 30 Brocken-
hurst Way, London, UK SW16 4UD.

Call 800/225-4876 (toll-free) 9-4
EST M-F to discuss microcomputer
interference problems. Free 40-
page product catalog. Electronic
Specialists, 171 S. Main St.,
Natick, MA 01760, 617/655-1532.

VOTEM, an analog interface, plugs
directly into 8K ZXs with no hard-
ware mods, allowing your computer
to measure voltage and temperature.
Price: $39.95 kit; $59.95 built 4
and tested. Down East also offers

6116 memory (2Kx8) to upgrade ZX8lis

to 2K for $11.95. Contact Down

East Computers, P.O. Box 3096,
Greenville, NC 27834.

aes Te

LJH now offers painted aluminum
keyboard enclosures to fit their
big keyboards. The 13xl0x4" case
houses one computer and 16K or 64K
memory pack. $45+$5 shipping ex-
cludes keyboard. LJH Enterprises,
PO Box 6305, Orange, CA 92667,
714/780-1422.

Get 16K-64K of directly addressable
RAM with Memotech's stackable mem-
Ory modules. Prices: 16K-$59.95;
32K-$94.95; 64K-S179.95. Another
plug-in provides high res graphics
with 192x248 memory- and bit-mapped
pixels, $149.95. A Centronics par-
allel printer interface works with
dot matrix or daisywheel printers.
It uses keyboard printer commands,
converts to ASCII, and can print in
lower case, $94.95. Memotech
Corp., 7550 W. Yale Ave., Denver,
CO 80227.

CONFUSING THE ISSUE

Radio Shack has discontinued
the TRS-80 4K color computer. Now
you can buy the 16K machine ($399),
BUT without Extended Color BASIC. i
Take care in comparing this machine :
to Sinclair's Spectrum specs, Ex-
tended Color BASIC adds 30 state- ‘
ments and 14 functions to COLOR
BASIC and you pay $99 more to get
them. Spectrum offers 16K and full
color control in the basic machine.

USERS' GROUPS

Here are the groups we've
heard from recently. If you'd like
to list your group, call 617/456-
3661 or drop us a note. We'll send
interested people in your area. To
locate a group, call or write (send
a self-addressed stamped envelope).
We'll send you the address of any
local group we know of.--AZ

ROAD TO RICHES

ROAD TO RICHES is an entertaining and educational
computer game in which up to four players are given

opportunities to invest in business ventures in an attempt to
increase their assets.
The program simulates a fast-moving world of investment

Central Virginia: Central Virginia in which you are confronted with all kinds of investments

Users' Group, Herb Miller, Rt. l ranging from conservative real estate opportunities to highly
Box 192, Troy, VA 22974, 804/589- risky Broadway shows.

8151 Pit yourself against a wheeler-dealer and see if. over a

period of seven years, you can come out on top. ROAD TO
RICHES is fun and informative, realistically portraying the risk
and skill of high finance.

16K $14.95

HANG MAN_=

We've created a Iéarning tool for you and your children which
contains seven versions of Hangman for the 2X81. Your child can play
against the computer's five pre-recorded libraries of categorized
words: Animals, Science, Countries of the World, States of America
and Fruits and Vegetables.

You can also play against opponents and the computer will request
players names and keep score.

The seventh option allows you to save. your own versions of
Hangman with up to 500 words each. This is ideal for parents to create
special spelling drills for their children.

As a special feature, each program picks a word from its own library
and compares it with the last 50 words played so you will not get

Pittsburgh, PA: Pittsburgh Area
Computer Club, Special Interest
Group--Sinclair, c/o Dick Welsh,
1605 Middlecrest Dr., Glenshaw, PA
15116, 412/487-0789.

North Suncoast, FL: Pasco-Hernando
Users' Group, John Dowlan, PO Box
5021, Spring Hill, FL 33526,
904/683-3961.

Atlanta, GA: Atlanta ZX80/81 Users

Group, c/o Phil Hoffstadter, PO Box 5

2842 ; Atlanta : GA 30301 : 40 4/2 96- eiaa co a running account of how many words you

8009 after 6 PM. 16K $14.95

a I Ee Ee ee Ee es a Ee
PLUS MANY MORE ZX81 PROGRAMS!

WRITE FOR FREE CATALOG

O Please send me copies of
ROAD TO RICHES @ $14.95 ea.
O Please send me copies of
HANGMAN @ $14.95 ea.

Mastercard/VISA #
Exp date

Please add $1.50 shipping & handling
New York residents add sales tax.
SEND CHECK OR MONEY ORDER TO

SOFTSYNG INC.

PO. Box 480, Murray Hill Station, New York, NY. 10156 (212) 685-2080

; Foreign orders must be paid by International Money Order or
Gladstone Electron ics, 901 Fuhrmann foreign draft in U.S. Dollars drawn on a New York bank.

Blvd., Buffalo, NY 14203, 716/849- NAME
0735, or 1736 Avenue Rd., Toronto,
Ontario M5M 3Y7, 416/787-1448.

Milwaukee, WI: Robert C, Harris,
5827 N. Maitland Ct., Milwaukee, WI
53217.

Chattanooga, TN: Chattanooga Area
Sinclair Users, c/o Dan Williams,
PO Box 1321, Collegedale, TN 37315.

San Diego, CA: Contact Robert
Jorgenson, 3814 Coleman Ave., San
Diego, CA 92154, 714/424-6202.

NEW CATALOGS AVAILABLE--FREE

ADDRESS

Se

CITY _

Softsync, Inc., PO Box 480, Murray
Hill Sta., New York, NY 10156,
212/685-2080.

STATE/ZIP

RR

64K MEMORY BYTE-BACK Co.
M- 64 $139.95 KIT ze

154.95 WIRED & TESTED
IN STOCK. SAME DAY SHIPMENT

All standard features included, plus lower 8K
of RAM can be disabled in 2K segments to
allow PROM or peripherals to be added.

EXPAND YOUR 16K SYSTEM $59: 95

If you have a Sinclair 16K RAM module and need
more memory, expand it to 32K and beyond by using
BYTE-BACK M-16 MEMORY MODULES.

You can’t connect two Sinclair 16K RAM modules together,
but you can connect one Sinclair 16 K and one or more BYTE-
BACK 16K modules to get all the memory you need.

THOUSANDS IN USE WITH PROVEN RELIABILITY

M-16 $59.95 Kit. $69.95 wired and tested.
IN STOCK. SAME DAY SHIPMENT

BB-1 Control Module. with 8 relays, 8 leds
&8 inputs. $59 Kit. 69 wire and tested.
WSTOCK SAME DAY SHIPMENT

MODEM with RS232 Port. $99.%; $119.95 wire

& tested.
90-Day Warranty On All Modules.
10-Day Return Priviledge

ORDER PHONE 803-532-5812

Add $4.95 shipping & handling to all orders.
BYTE-BACK CO. alle eas
Rt.3. Box 147 Brodie Rd. cml) Zn!
LEESVILLE, SOUTH CAROLINA 29070

HOUSEHOLD FINANCES--8K/16K

This program can help put your
household finances on a business-
like basis. It requires 8K ROM and
16K RAM.

To conserve memory for data,
the set-up procedure is done in the
immediate mode, thus using no pro-
gram storage space. Type in the
program (ignore inverse video in
line 630; the computer switches it
after a save and reload), then
follow these steps:

1. Type DIM AS$(10,13) and press
ENTER or NEWLINE.

2. Type in this program:

800 FOR K=1 TO 10

810 INPUT AS$(K)

820 NEXT K
Press GOTO 800. Then type in 8
expense categories, such as FOOD,
HOUSE, AUTO, and so on, pressing
ENTER or NEWLINE after each. Use
the last two categories for income,
such as SALARY and BONUSES. Each
category can have up to 13 charac-

ters. After entering your cate-
gories, delete lines 800-829.
3+ Press GOTO:10. Your 10 cate=
gories will come up with corres-
ponding letters.
4, Select M (for CLEAR MONTH)
N (for CLEAR YEAR).
You're ready to go. The program is
self-saving (option L) and self-
starting on reload to protect data
from accidental erasure by RUN.
After viewing a statement
tion K),
the menu.
With a 16K RAH, this program
leaves you about 12.6K bytes to
fill. The inverse characters are
HOUSEHOLD FINANCES in line 20 and
CURRENT STATEMENT in line 150.

then

(Op-
press CONT to go pack to

Variables and Strings

A$ category name array

A(K) monthly array

B(K) yearly array

K For/To (primary)

J For/To (secondary)

M(J) Print scratchpad

Q Monthly total R annual total
S Address T Line pointer

U Tab pointer ZS Entry string

James W. Holder,

Huntsville, AL

E : 3 be
TRE 14; "H=CLEAR MONTH FRB |; "l=
SAVE" >) TRS 34; UN=CLERR YEAR’; AT a
& ,@,° INSURANCE BSENEFITS RARE NEGA
JTIVE.NEGAT IVE BALANCE | SHOWS BENE
FITS EXCEED PREMIUMS.

3@ INPUT £5

40 IF COPE 28=48 THEN GOTO 128

S50 IF COPE S§=-49 THEN GOTO 622

6@ IF COPE 2#=Sa THEN BIN ATL
3

7@ IF COPE 2$=S2 THEN PIM Btls
3

SB@ IF CObeE 38:47 THEN GOTO 3&

Q]@ LET RtCQPE 2Zs-SB ri =Aticope Zs
-GYIHVAL Zsti TO 3

1@@ LET Bicoce Fe-sF:=eicope zs
-S7P)IHURL 28i2e Ta :

12@ CLs
13@ DIN #H

E

Rie.
118 GoTa 382

tft
14@ LET 3=358

FOR vG=si Fo 2
Mid) <8 FHEN GOTO 25a
Mid) «Lees THEN LEFT Usl+

ABS Mii) ¢Leee FHEN LET VU
RES Nivdis ¢2@& FHEN LET Ue
ABS Midi <2 THEN LET Us
BT J ,b8s Mis83

IF
PRINT

a
K=8 OR S=<46G O88 S=54AQ Th

28 PRINT AT T.8; “TOTAL EXPENSE
STAB er TAB 12; °.88 $°:; TRE

PRINT AT T.
1437S"; TAB.

8
LET Mtlishi
LET Nt2ei =6 ¢

“TOTAL INCOME"

TRE 2

PRINT AT T.&; VPROF IT “LOSS”
: "BITRE 1298;"°.88 a8"

=A 19) +A 018) -5
Mize ar tB}4H 018) -R

“PREPARE TO SF
FOUC

PRINT AY 6,8;
aH ele eile RUNNING;
“640 PRUSE aaa

650 SAVE “HOUSEHOLD F INANCER"
6608 GOTO 18
SYNTACTIC SUM: GaO53, SK

WANT A SINCLAIR PRINTER but don't
want to wait or send to England?
Check Gladstone's new catalog--ZxX
printer $135 US or $169.95 Can.
Gladstone Electronics, 1736 Avenue
Rd., Toronto, Ontario, M5M 3Y7,
416/787-1448.

I TRB 2S

BEGINNERS' BASIC--MORE ON INKEYS$

As we saw in May 82, the 8K
ROM's INKEYS function "watches" the
keyboard and looks for a keypress,
When used with PAUSE, INKEYS tells
the computer to wait for the user
to press something.

You can use INKEYS to either
make the computer stop program
execution if any key is pressed,
stop unless any key is pressed.

In either case, remember the
PAUSE statement that makes the
computer wait. Because you want to
control when the program stops or
continues, use a nice big value
like PAUSE 40000. This gives you
enough time to choose what to do
before the computer goes on without
you--the bigger the value, the
longer the PAUSE.

To stop execution if any key
is pressed, add a line like this
after the PAUSE statement:

100 IF INKEYS<>"" THEN GOTO 100
This line checks to see if any key
is pressed. The null string ("")
means no key. Thus any keypress at
line 100 (making the IF part true)
causes the computer to GOTO 100.

As long as you hold a Key, the
program loops back on itself at
line 100. This "holding pattern"
effectively makes the computer wait
until you let up on the key.

This method also lets you
program a keyboard-controlled
reset. At any time in your pro-
gram, you can insert a PAUSE and
INKEYS$ combination to allow the
user to stop using the program or
to start over. Change line
100 to IF INKEYS<>"" THEN STOP to
end the program. Or uSe IF
INKEYS<>"" THEN GOTO the first
program line.

To stop execution unless any
key is pressed, use this line:

100 IF INKEYS="" THEN GOTO 100
Here the null string, or no key,
causes the computer to stay at line
100. Now the computer waits until
a key is pressed (so INKEYS does

or

not equal "") to go on,

KEYBOARD SCANNING FROM MACHINE CODE

One of the problems you must
solve when writing machine code for
a ZX80/1 with 8K ROM is deciding
how best to scan the keyboard.
Although there is a Keyboard Scan-
ning routine at 02BB and a Keyboard
Decode routine at O7BD, it is pref-
erable on the whole not to use
either of these directly.

In SLOW mode, the system vari-

able LAST K (dec. 16421/2, hex
4025/6) holds the "key-value" of
the last key pressed. Pressing a
key forces an exit from the display
routine after the Keyboard Scanning
routine has detected that a key was
pressed,

This Key-Value Demonstrator
program shows the key-values for
the ZX80/l's different keys:

REY -VALUE DEMONSTRATOR
if SCROLL).

ee PRINT toe ne YY; PEEK 164

BLISSE2PEEXK 1642
Ga GOTO 12

SAMPLE RUN

65535
65015
6453
63479
61431

& ihe

You'll see the key-value for no-key
is 65535, for 1 is 65015, and so
on.

Knowing these values ina
machine code program in SLOW, you
can read the system variable, LAST
K, and match it against known key-
values. Or you can stay in a loop
until you press a certain key.

This method works well, but you
have to be careful with multiple
keying.

To use this method, you must
be sure the machine code program is
in the SLOW mode. How can you
select FAST and SLOW from machine
code?

You can select SLOW by calling
either OF28 (old 8K ROM) or OF2B
(improved 8K ROM--new 8K ROMS
should be improved). Select FAST
by calling OF20 (old ROM) or OF23

(new ROM). Because some people may
have old ROMs, I use this construc-
tion for FAST/SLOW selection to
make my program ROM-independent:
START LD HL,+NEXT 76 bytes
further on
PUSH HL ;push address
onto stack

LD HL, (SLOW 7 SLOW=0CAC

or FAST) FAST=0CAF
JP (HL) scall SLOW or
FAST

NEXT eeeeeoee

snow proceed

This routine works by looking
up the appropriate address in the
"Darameter table." Note that call-
ing SLOW is really "going to SLOW
mode" if it is available and work-
ing.

The FAST/SLOW Keyboard Scan-
ning program following is my
preferred method of keyboard scan-
ning. It is a copy of Sinclair's
method and so has the same "feel"
as obtained when entering BASIC.

The machine coding is cunning
as it uses an apparently never-
exited loop:

O04CF SLOW-DISP BIT 0,(HL)
JR 2Z,04CF,SLOW-
DISP
The answer is that in SLOW mode,
bit 0 of (HL) becomes set whenever
a key is pressed,

This machine code routine also
caters to multiple-keying and sets
the debounce mechanism to its cor-
rect value. Note the routine is
set up to return the character code
of the unshifted key being pressed.
It is printed using a D7 instruc-
tion only for for convenience of
the demonstration.

19 REHM iSSAREGPTSOR LS RASS PaSGeID
AS567S9G 122456
S& REM NOL ENTER THE ROUTINE

s& LET ra

S2SSFCEDABSS4 OCECOFDCESBS6SEFFS22
FLOCDEDO?TSGEGAGTSDTCS™

40 FOR f=2 Ta 36

SO FORE iSSistA, Rs fifOPe ASlAax
S-23 -BE} +COHeE Ass {e223 -BS

&G NENT &

¢ REM NOL COLL THE ROUTINE

BCROLL
RAND USER 26514
GOTQ Lee

Logan, Skellingthorpe, England

‘SLEBAGCBVPECCS9@2RACBE4

Imagine building your own computer
for only $79.95!

That’s exactly what you can do with
the ZX81 kit. It comes with all the parts
you need and complete diagrams and in-
structions for putting it together. All you
have to supply is soldering iron, solder,
and a screwdriver. Plus, of course, a little
bit of work.

But you get a lot more than several
hours of kit-building fun. You also get a
surprisingly powerful personal computer.
The ZX81 hooks up to any TV for a 32-
character by 24-line display (we provide
the connecting cables). You can also use a
standard cassette recorder to store your
programs (again, we provide the cables).

Most important, you get a BASIC pro-
gramming language that’s powerful
enough to challenge and interest the
most experienced programmers. The
ZX81 can handle multidimensional string
and numerical arrays. It has full mathe-
matical functions accurate to eight deci-
mal places. Single-key entry for every
command. Syntax error detection, de-
bugging codes, and easy editing. Plus

features that are ideal for creating games,

such as 20 graphic symbols, continuous

Build your own computer for $79.95

nee Cat
NOE
ae were

The Sinclair 7X81 personal ae kit

display, and random number generator.

The ZX81 can be expanded too. You
can increase the memory from 1K to 16K
with our Memory Module for $49.95.
And you get a comprehensive manual
that completely documents the capabili-
ties of the ZX81, and teaches program-
ming from the ground up.

In short, you get all the features that
have made the Sinclair ZX81 the fastest
selling personal computer in the world.
And you get the satisfaction and fun of
building it yourself.

A few years ago, this kind of computer
power was simply unavailable to the
individual. Even today, most personal
computers are too expensive to buy for
personal use.

But the ZX81 kit can be yours for only
$79.95. Take advantage of this unique
offer today. To order, send the coupon
along with a check or money order. Or for
faster delivery, call our toll-free number
and use your MasterCard or VISA.

To order call toll free: 800-543-3000.
Ask for operator #509. In Ohio call: 800-

582-1364; in Canada call: 513-729-4300.
Ask for operator 4509. Phones open
24 hours a day, 7 days a week. Have your

MasterCard or VISA ready.

These numbers are for orders only. If
you just want information, please write:
Sinclair Research Ltd., 2 Sinclair Plaza,
Nashua, NH 03061.

[ 40 CODE | MAIL TO: Sinclair Research Ltd.,
One Sinclair Plaza, Nashua, NH 03061.
PRICE* QTY. AMOUNT

ZX81 Kit

16K Memory
Module

| Shipping and
Handling

| Name

[Adaress

Sinclair technology is also available in Timex/Sinclair
computers under a license from Sinclair Research Ltd.

— | jm | oo | — ||

SIMPLE 4K-8K ROM SWITCH

I received the 8K ROM upgrade
for the ZX80 and was disappointed
to find that I could not load pro-
grams in integer (4K) BASIC. I
interchanged ROMs, and of course, I
soon bent some terminals. Faced
with the prospect of many hours of
rewriting, I decided there had to
be a better way. There is! In the
Sept. 1981 Microcomputing is an
article entitled "DOS Mod" by Scott
King. Borrowing his idea, here is
how to run integer and 8K BASIC in
your ZX80 without unplugging ROMs.

First, be aware that static
electricity can instantly destroy
ROMs; observe these precautions
while working with them. Both you
and the surface you work on must be
grounded. Attach a flexible copper
wire to the central screw holding
the face plate of a grounded wall
receptacle. Strip 2" of insulation
off the free end. Keep this wire
in contact with your body during
the modification procedure. Loop
the bare end around your wrist, or
ankle or tuck it in your shoe, but
remember to unwind when you leave
the work bench! Next, spread a
sheet of aluminum foil over the
working surface,

You will need a grounded (3-
wire) solder iron witha fine tip
(less than 1/8" diameter), needle
nose pliers and fine wire cutter
and stripper.

Use an ultra-miniature single-
pole switch you can fit inside the
ZX80 case when mounted on the lid.
Radio Shack sells a Suitable part.
You will also need electronic-grade
roSin-cored, fine-gauge solder and
9" of 30 gauge insulated wire.

Remove the cover of the 2X80.
Use a small screw driverto lift
the ROM from its socket by prying
up not more than 1/32" at each end.

Each ROM is coded at one end
with a recess, dimple or dot on the
top surface. Arrange this feature
to point away from you. Pin #24 is
now furthest away and to the right

of the key-feature. Gently bend
this pin up using needle nose
pliers. Do not lever against the
ROM package, rather, squeeze the
bend in the terminal to straighten
it. Repeat for the second ROM.

Pin #24 is Vcc or the positive
power supply for the ROM. Switching
current to this terminal activates,
and interrupting, disables the ROM.

You received your 8K ROM with
terminals imbedded in conductive
black foam. If you still have it,
use it for the next steps.

Insert one ROM into this foam
pad up to the shoulders of the
terminal. Place the second ROM
Piggy-back as shown in the drawing.
Align the pins carefully and make
sure the lower ROM pins spread out-
ward to contact the socket. Tack
the ROMs together except at the two
pins #24. Use an absolute minimum
of solder. Do not allow solder to
run below the shoulder of the lower
ROM pins or you can't re-insert the
assembly in its socket. The foam
helps control the solder. If you
are unsure about this step, try it
on old ICs.

Inspect for shorts and remove
excess flux with a Q-Tip dipped in
alcohol. Vodka will do. With the
key-pad closest to you, the dimple
on the ROM packs should point away
leaving the two pins #24 to your
right. Re-insert the dual ROM
assembly in its socket.

Check your connecting switch
for size. There should be room to
mount it inside the 2X80 case just
"north" and slightly "east" of the
ROM assembly. Make sure that with
the switch mounted and lid closed
nothing touches the PC board! I
needed to trim about 1/16" off my
switch terminals.

Mark the switch position on
the lid and drill a mounting hole.
in the latter. I sawed about 1/4"
off the toggle to reduce its
protrusion from the case surface.
Mount the switch; this locates it
with the lid laid beside the 2X80,
about 3" from the ROM assembly.

Software Breakthrough!

Cut three 3" lengths of 30 * covey as
gauge wire. Strip and tin 1/16" of “a.
each end. * Joystick +i

Leading into the ROM socket at $1495 4 ia
pin #24 find a wide printed circuit 2 r xe
conductor run. Quickly solder one sdk chacnrad a
wire to this run on the PC board. mea a
Don't overheat the PC board. The $69 qo
other end of this wire goes to the %* Keyboard i i
common, usually central, post on $7495 x.

the switch. Connect the other two fullsize assembled

wires between each switch pole and panera
ae é;
She tho ins. 124 cea cking oue econ RUNS WITHOUT ANY HARDWARE MODIFICATIONS

1) Use with or without our joysticks. 5) 100% Machine Code
* 2) Real time Animation r
the ROM assembly, | ae aaa anus
Carefully replace the 2X80 lid 4) Auto Run 8) 16K Required

taking care not to pinch or break a
wire. Power-up your system and see THE INNOVATORS
which switch positions correspond ARE COMING

to integer and 8K ROMs. I suggest
you disconnect your power supply Call or Write for more information

pefore switchi ng between ROMs. You American Express, Visa, Master Charge, Money order, pc (allow 2-3 weeks to clear)
can not, of course, load a program iiitcis eatin Goce cade a alee tal
into RAM and then switch ROMs. Visit our Showroom 10:00 - 6:00 Monday thru Saturday

MICROCOMPUTERS PLUS, INC.
Martin Oakes, Freeport, IL | : GALESBURG. IL 61601
PHONE: (309) 342-9572

if viewed from a distance. To
change the bird's speed, change the
PAUSE statements (lines 45 and 55).
If you delete 45 and 55, it
resembles a bat.

Mike Hastie, Concord, MA

This listing is printed on CAI's
40-column printer in regular mode.
For a full review of the printer,
see page 20.--AZ

ut ut

FLYING BIRD

This short 8K routine shows
how to put graphics in motion. It
displays a flying bird, seen best

PRODUCTS THAT SUPPLEMENT NATURE’S COMPUTER

WE HAVE THE PRINTER

The MW100 is the only plain
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U.S. for the Sinclair ZX81, at
$119.95.

. .. provides hard copy
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. .. produces hard copy of
program listings, useful
when writing programs
.. . prints 16 characters per . .. connects to the rear of
line, lets you print every- the computer, so you can
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The MW100 easy to use software
. ..uses 134” plain paper and commands ...full instructions supplied
a standard ribbon cartridge ;
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mal printer L Print, and Copy. a 90 day warranty.

WE HAVE THE PROGRAMS

MATRIX PLANNER-16K
An “electronic spreadsheet”
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Hardware required: 16K

SPACE INTRUDERS-16K
Play the world famous
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ware required: 16K

GULP-16K

Everyone’s favorite game of
maze pursuit and counter-
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Hardware required: 16K

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ITEM PRICE TOTAL

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CODE MONITOR-16K
Here is the tool to help you
direct your machine through
the forest of machine code
and hexadecimal. Test
machine-code instructions
in operation. Examine the
ROM and see how any
BASIC statements you
write are stored in the RAM.
Comes with a detailed

user manual. Hardware
required: 16K

CHESS-1K

Displays board positions
and keeps separate records
of plays made. Hardware
required: 1K

You can pay by check, Visa or MasterCard.

Fill in your complete address in detail and
include your zip code. Please allow six to eight
weeks for printer delivery.

PAYMENT METHOD

MW 100 PRINTER $119.95

MW 100 SHIPPING
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MATRIX PLANNER

DATA BASE/FAST FILE

L] CHECK ENCLOSED
VISA

ia MASTERCARD

ACCOUNT NUMBER

1 E:

GULP

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SOFTWARE TOTAL

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SIGNATURE

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_

DEAR EDITOR

I wrote a small machine code
monitor for my 1K 2X81. Everything
works fine but I must go back and
forth to BASIC to get into and out
of FAST mode (cassette operations
only execute in fast mode). How
can I do this within my monitor?
Clark A. Calkins, Walnut Creek, CA.
To call FAST: Jump to OF23. This
is a ROM subroutine, ended by RET.
To call SLOW: Call OF2B which
jumps to 0207 which returns follow-
ing 0226.--KO

The newly released Fujitsu
MB8416 2Kx8 bit random access mem-
ory makes it easy to expand the
Sinclair "on-board" RAM to 2K.
Since the MB8416 has the same 24-
pin configuration as the 4118 RAM,
just move jumper Ll to the L2 posi-
tion and insert the new RAM in
exactly the same position as the
old one.

If your ZX81 comes with two
2114 RAMS, replace the 18-pin
socket at the IC4a position witha
24-pin one (try the Augat 524AG11D
or the Radio Shack 276-1989 sock-
et). (SYNTAX suggests uSing a 28-
pin socket around the existing 18-
pin socket.--KO) Then move the
jumper and install the new RAM,
Don't bother removing the second 18
pin socket at the IC4b position,
just leave it empty. Be careful
not to lift the printed circuit
foil when removing sockets.

This change is easy because
Fujitsu's MB8416 is a static RAM.
It does not need the extra pins
required to refresh dynamic RAMs
like the 4816 (not to be confused
with the Fujitsu MB8416) recom-
mended by Sinclair for expanding
ZX81 memory. So you don't need a
new IC socket if a 24-pin one is
already installed. Also the static
RAM appears to be easier to get to
work properly than the dynamic type
(see Jan.82, p.12).

Some readers may find parts
available only at distributors with
large minumum orders. Most dis-
tributors will waive this rule if
you pay for everything in advance,
including postage if necessary.

New England readers should
call Comp Rep Associates, Westwood,
MA at 617-329-3454 for information
on stocking distributors nearest
them. Others can contact Fujitsu
Microelectronics 1841 Hicks Road,
Suite D, Rolling Meadow, IL 60008,
312/934-6400 or Fujitsu Microelec-
tronics, 2985 Kifer Road, Santa
Clara, CA 95051, 408/727-1700. One
MB8416 costs about $13.50 and the
socket between 79¢ and $2.85 de-
pending on the type you get.

William D. Jordan, Boston, MA

P.S. I have just discovered that
besides MB8416, Fujitsu makes an
even cheaper RAM, the MB8128. It
sells for $11.50 each in quantities
of 1-24. It is equivalent to both
the Fujitsu MB8416 and the Hitachi
6116. I tried one in my Sinclair
ZX81, and it works quite well.

The MB8128 is a very good
value since it costs slightly more
than half the price of comparable
RAM's offered for the Sinclair
ZX81. When ordering, use the full
catalog number, MB8128-15. The -15
stands for 150 ns access time,
adequate for this purpose.

Is it possible to disable the
SPACE-key interruption feature
during critical stretches of code?

Is it possible to disable
screen clearing for the CONT
command?

C. Alfred Spencer, Franingham, MA

Put your critical routines in
machine code and call them with the
USR function. The BREAK function
will not work until you return to
BASIC. I don't know how to prevent
screen clearing after CONT. Try
using SCROLL to avoid CONT.--KO

I'm a confused newcomer and
would appreciate help! What is the
meaning of the numerical value of
the Syntactic Sum? For example,
in VoOl.2 no.12 p.l7 is a sum of

"53215, 8K". 53215 what? It can't
be 53.215 bytes. What then does it
mean?

Julian M. Goldman, Brooklyn, NY

The 8K Syntactic Sum program adds
the codes for every byte in the
computer's BASIC program area.
This sum changes if any character,
keyword or line length changes. So
if you type 1 where we typedI,
you'll get a Syntactic Sum differ-
ent from the one we publish. Any
change except reversing two letters
alters the sum.

8K Syntactic Sum was first
published in Jun.81; 4K in Feb.81.
If you don't have a copy, send us
an SASE. See also Fred Nachbaur's
letter following.--AZ

When using the 8K version of
Syntactic Sum on ZX81s, the machine
must be in FAST mode when calling
the subroutine with PRINT USR 17376
(or 32736 with 16K RAM.) If the
subroutine is called in SLOW mode,
the machine invariably crashes.
Switch to FAST before entering
PRINT USR 17376 (or 32736 for 16K).

If your BASIC program contains
a SAVE command, the Suntactic Sum
will be less than its true value by
128 before the SAVE command has
been executed. This is because
after the SAVE is executed, the
last character in the label
changes to its inverse form (see
ZX81 manual, p.81). So to use
Syntactic Sum to verify correct
entry after typing in a program,
first make the computer execute the
line(s) containing SAVE before
calling the SS routine. Or man-
ually change the last character in
SAVE statements to inverse video.

Finally, the oriqinal Syntac-
tic Sum article warns against
typing NEW after Program 2 has run.

13

On the ZX81, you may use NEW to
your hearts content once the
Syntactic Sum program is safely
tucked away beyond RAMTOP (see
ZX81 manual chap.26). NEW clears
memory only up to RAMTOP; since the
computer has been fooled by Step l
into thinking it has 31 bytes less
than it actually has, NEW will not
remove the ML program. To erase
Syntactic Sum, POKE 16388,0 and
POKE 16389,68 (or 128 for 16K),
then NEW. Or simply reset the
computer by pulling the plug.

Fred Nachbaur, El Monte, CA

I am working on an add-on for
my Microace with 8K ROM to enable
it to use the SLOW mode. It ap-
pears to work, but with one big
defect: in SLOW, all characters
are printed with the bottom part
above the top part. I would like
to hear from anyone who has any
idea on how to solve this problem.
If I ever get the circuit to work,
I will send plans for it it SYNTAX
so other people with a Microace or
ZX80 can use ZX81 software.

Jason Harper, Rt. 1 Box 3,
Sylvester, TX 79560

ZX80 owners--can you help?
ATTENTION SUBSCRIBERS

Some makers and distributors
of ZX-related and other products
have asked about mailing literature
to SYNTAX subscribers. We think
you would find some of these
products useful or interesting.

However, we consider your name
and address to be private. If you
would not like to receive litera-
ture in the mail, please inform us
in writing. Send your letter to
SYNTAX, RD 2 Box 457, Harvard, MA
01451. If we do not hear from you,
we will presume that you would like
to receive information from other
manufacturers, distributors and
publishers in the mail.--AZ

NUMBERS HELD INEXACTLY ON THE ZX81
(Fifth and final part of a series)
FOR-NEXT Loop Counters:

The use of non-integral FOR-
NEXT loop counters is a powerful
facility. The principles discussed
previously should help you use them
as your servant, not your master.
For example, how would you

amend this loop to print the inte-
gers 0-10? Before reading the
answer, RUN this routine and try to
work out what is wrong:

10 FOR X=0 TO 1 STEP .1

20 PRINT INT (10*X;

30 NEXT X
One answer is:
FOR X=0 TO 1.05 STEP .1
PRINT INT (10*X+.5)

30 NEXT X
This illustrates that floating-
point systems (like the 2X81)
require you to slightly over- or
under-state numbers to make the

10
20

arithmetic work. The amended line
20 rounds to the nearest integer;
amended line 10 overstates the loop
limit a littl2 for safety.

You will often need to round
an integer N yet again for safety
by LET N=INT (N+.5).

Last Note:

I mentioned a subtraction
quirk. Even with the amended ROM,
332-1 rounds 53 hey ont32
rounds to 2%t?4,

PRINT 14+2**-32-

gives 4.6566129E-10 (WHICH “is: 2° "=,
not 2 7“); .5 is held as (1/2)-
(1/293, but PRINT (1/2)-.5 gives

2.3283064E-10 (which is not 2
but 2°“; and so on. No doubt this
"rounding" was done to save bytes.
Now you have enough informa-
tion, I hope, to be able to cope
with it, and not be thrown. By the
way, 2>“-l is given accurately by
2**32-2+1.
Frank O'Hara,

Surbiton, UK

Surrey,

ZX81 OWNERS with 16K RAM!
IT'S READY--~ARE YOU?

FI
couse $14.95 +
If_so, you get: :
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*Nearly 2K of machine code
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*A\ 4K Star Atlas as the moving
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*Q-each fuel and skili levels that
are interlocked for more "reality"
*4 ways to lose---no fuel, no oxygen,
no gun power, or no shields. 1 way
to win---destroy ALL enemy craft.
*An enemy data generator imbedded in
the run as part of the "action"

*"Blink"-less pauses in BASIC

*Stick-on/peel-off custom keys

*In-depth booklet explaining both
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*Shipped on a certified cassette
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| ZETA Software/PO Box 3522/Greenville,SC 29608
lEnclosed is $ Eli eto| eae CO | ene ee
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pe lus $2.50 S&H for the order.

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Please allow 4 weeks if paid by check.

14

MC PROGRAMING: PUSHING AND POPPING
(Part 7 of a series)

In the 4K (ZX80) ROM, the
System Variables are at addresses
16384-17423. When processing input
Or program lines, the Z80A central
processor uses the IY register pair
"indexed" at 16384. In other
words, the system variables area is
IY's storage for control data.

While you can use any RAM
address for data storage, avoid
these addresses:

1- 16384-16423 System Variables

2- An address-pair that must hold a
line number for a statement
(such as 16424-16425--first
program line)

3- Any address-pair to be
displayed.

ZX80s won't accept a statement
without a "function" so the only
place left to store data and
machine code subroutines is in REM
lines, preferably at line l.

However, addresses are not the
only place to store data. Regis-
ters hold data without needing
addresses but only 10 pairs are
available, so the 280 keeps regis-
ter-stored data in the Stack.

This Last In-First Out "box"
is an ideal place to hold transient
data during processing. But while
it is the easiest storage area to
use (only two l-byte instructions
to access it), it is also the easi-
est tool to crash your MC program.

Unfortunately, ZX80 already
stores data in the registers you'll
want to use. If you "erase" cer-
tain data...ZAP! Scrambled screen.

Solution: PUSH a register
pair before you use it and POP it
before RETurning to BASIC. PUSH
means put data onto the Stack; POP
means pull it back off. The com-
mands for these functions are of
the form PUSH qq and POP qq where
qq is a register pair (IY, IX or
another). Check Appendix A of the
ZX81 manual or a 280 programming
book for codes. Three rules:

1- PUSH the register pair before

SYNCHRO-SETTE

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you use it.

2~ POP the data back into the
correct register pair before
RETurning to BASIC (C9).

3- Make sure you have one POP for
each PUSH: don't push more data
than you will POP, and don't POP
more data than you have PUSHed.

Remember the Last In-First Out

rule: each time you PUSH data, it

goes on the top of the Stack. When
you POP it, it comes off the top of
the Stack,

Next month: CP TESTS FOR BRANCHING

Jon Bobst, Zeta Software, PO Box

3522, Greenville, SC 29608-3522

CORRESPONDING ADDRESSES FOR 2X81:
Systems Variables 16384-16508
First BASIC line No. 16509-16510
Also, Sinclair warns against
using A',F',IX,IY, and R register
when using SLOW mode. When you
return to BASIC, you must be sure
ITY¥=4000h and I=001Eh.--KO

TIC TAC TOE--4K/2K

This game runs on a 4K ROM
with at least 2K RAM. Enter the
program and RUN. Choose who goes
first (input starting with a Y=Yes;
anything else=No) then enter the
number of the square you want to
mark. The ZX80 displays your move
and itsown. Its first two moves
are chosen at lines 650-750. All
others are forced or random. When
the game ends you can play again.

Lines 180, 190 and 200 contain
directions for entering graphics
(eg., line 180: type 3 spaces,
shift Q, 2 spaces, shift Q, and 2
spaces in the quotation marks with
no extra spaces or commas).

Raymond Fowkes, Coalinga, CA

10 CLS

20 PRINT ,"TIC TAC TOE"

30 PRINT

40 PRINT "DO YOU WANT TO GO FI
RST?"

50 INPUT A$

60 LET Q=CODE (A$) =62

70:4ELS

80 PRINT ,"TIC TAC TOE"

90 PRINT

100 PRINT

110 LET X=1

120 GO SUB 180

130 GO SUB 210

140 GO SUB 180

150 GO SUB 210

160 GO SUB 180

170 GO TO 240

180 PRINT ,"3sp shiftQ 2sp shiftQ
2sp"

190 PRINT ,"1sp";X;"1sp shiftQ"
;X+1;"1sp shiftO";X+2;"1sp"

200 RETURN

210 PRINT ,"ShiftF 2shiftw";
CHR$ (133) ;"2shiftW33";CHR$ (133);
"Qshiftw"

220 LET X=X+3

230 RETURN

240 RANDOMISE

256 LET A=0

260 LET C=-1

270 LET P=-1

280 DIM C(4)

290
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
450
460
470
480
490
500
510
520
530
540
550
560
570
580
590
600
610
620
630
640
650
660
670
6 80
690
700
710

DIM P(4)

IF Q THEN GO TO 860
LET Y=RND(5) *2-1

GO TO 780

IF C<1 THEN GO TO 530
FOR B=0 TO C

FOR D=0 TO C

LET X=C(D)

LEP Y=C(B)

GO SUB 1030

IF Z THEN GO TO 510
GO SUB 1050

GO SUB 1070

IF PEEK(A)THEN GO TO 510
GO SUB 1190

PRINT

PRINT "--I WON--"

PRINT

PRINT "PLAY AGAIN?"
INPUT A$

IF CODE(A$)=62 THEN RUN

LIST

NEXT D

NEXT B

FOR B=0 TO P
FOR D=0 TO P
LET X=P(D)
LET Y=P(B)
GO SUB 1030
IF Z THEN GO TO 630
GO SUB 1050
GO SUB 1070

IF PEEK(A) THEN GO TO 630
GO TO 820

NEXT D

NEXT R

IF C>-1 THEN GO TO 680

LET Y=5-2* (P(0)=5)

GO TO 780

IF C>0O THEN GO TO 770

IF NOT Q THEN GO TO 730

LET Y=1

IF E=1 OR F=6 OR E=8 OR P(0

)=6 OR P(0)=8 THEN LET Y=9

vm,

IF ABS (E-P(0))=8 OR (E AND

P(0))=3 THEN LET Y=RND(4) *2

720
730
740

GO TO 780
LET Y=10-C(0)
IF (E/2)*2=E OR E=10-C(C) T

HEN LET Y=5

750
}*2
760
770
780

IF C(0)=5 THEN LET Y=9+(E=9

GO TO 780
LET Y=RND(9)
GO SUB 1050

790
800
810
820
830
840
850
860
870

880
890
900
910
920
930
940
950
960
970
980
990
1000
1010
1020
1030

LET Z=Y

GO SUB 1240

IF PEEK(A) THEN GO TO 770
GO SUB 1190

LET C=C+1

IF C>3 THEN GO TO 1000

LET C(C)=(Z-29-(2/70) *45) /3
INPUT E

IF E<1 OR E>9 THEN GO TO 86

LET Y=E

GO SUB 1050

LET Z=Y

GO SUB 1240

IF PEEK(A) THEN GO TO 860
POKE A,6

POKE A+1,6

POKE A+18,8

POKE A+19,6

LET P=P+1

LET P(P)=E

IF P<4 THEN GO TO 330
PRINT

PRINT "--TIE GAME--"

GO TO 460

LET Z=( NOT X<Y OR Y=X-5-10

TiS) OR Va 10= (i45* (225):) * 2.08

(X/2)

/2))
1040
1050
1060
1070
1080
1090
1100
1110
1120
1130
1140
1150
1160
1170

*2=xX AND (Y=5-X/2 OR Y=10-X

RETURN

LET Y=Y*3+29+((¥-1) /3) *45
RETURN

LET X=X*3+29+((X-1) /3) *45
LET Z=2*Y-X

GO SUB 1170

IF A THEN GO TO 1150

LET Z=2*X-Y

GO SUB 1170

IF A THEN GO TO 1150

LET Z=(X+Y) /2

GO SUB 1240

RETURN

LET A=(Z=32 OR Z=35 OR Z=38

OR Z=86 OR Z=89 OR Z=92 OR Z=14

0 OR
1180
1190
1200
1210
1220
1230
1240

Z=143 OR 2=146)

RETURN

POKE A,3

POKE A+1,6

POKE A+18,133

POKE A+19,2

RETURN

LET A=PEEK (16396) +PEEK (1639

7) *256+2

1250

SYNTACTIC SUM:

RETURN
27909, 4K

GRANDSON OF BIG CHARACTERS

John Filley's Son of Big Char-
acters (Feb.81) works only on 4K
ROM. Here is an update for 8K
ROM/1K RAM. The graphics charac-
ters are now in a logical order, so
you need no REM statement. But,
the Boolean operators AND, OR and
NOT no longer operate as bit mani-
pulators as in John's program (ie.,
Q AND B). Lines like 100 and 102
replace these operators.

This program can display 2
lines of 16 characters in 1K. For
inverse video, add 128 to line 110:

110 PRINT CHRS (ABS (128+C+4*D
+2*E-F*135));

William Wentz, Rio Rancho, NM

NOW AVAILABLE

keyboards

Standard Computer Keyboard Designed
for ZX81, ZX80, & MicroAce

e« Same switches used on Apple Computers
¢ Two shift keys «¢ 6-inch space bar

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Prices Subject To Change

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(714) 780-1422 Visa & M/C Accepted

IMPROVED DATA INPUT

The way the ZX81 accepts input
during program runs is not great
compared to most computers. This
subroutine improves input using
INKEYS. Use it in your programs to
enter data at any screen position
instead of the bottom line. Data
stays on the screen after entry.
The subroutine gives a blinking
cursor to show the current entry
position and you use RUBOUT and
NEWLINE (ENTER) as usual.

As noted in SYNTAX, subrou-
tines run faster when placed at the
beginning of a program. It's par-
ticularly important that this sub-
routine be the first thing ina
program, or you get a noticeable
delay when pressing keys. The only
line before this subroutine should

18

be a GOTO to the main program
start. In fact, the subroutine
begins after the RETURN because the
first lines are executed only once.

Use GOSUP 400 instead of INPUT
statements. A blinking block cursor
appears on the screen at the cur-
rent print position (determined by
the last PRINT statement). Enter
data, using RUBOUT to erase the
previous character. Use NEWLINE or
ENTER to end the data string. The
subroutine returns the input data
in the variable CS. This is a
string variable, so if you want
numeric data, use the VAL function
to convert it.

Lines 190-230 wait for a key-
press and blink the cursor. When
you first call the subroutine Pl
and P2 are set to the current
screen print position by PEEKing
the system variable S POSN. S POSN
(at 16442) holds a value equal to
33 minus the current column and (at
16442) to 24 minus the current row.
P3 switches between 1 and 0 using
the NOT function to generate the
cursor. Line 320 prevents exiting
the subroutine without a keypress
other than NEWLINE.

Nels J. Anderson, Chestnut Hill, MA

288 LET CS =CS+AS

272 PRINT AT PL. P2: As

18@ LET Pe=Padi

49@ IF INKEYS<3"" THEN GOTO 196
S@02 LET PO=sNOT PS

SLA IF INKEYS<)"" THEN GOTO 24m
S28 PRINT AT Pi, Pe, CHR (Posies
¥

230 IF INKEY&S="" THEN GOTO 2e¢
S4@ LET AS=INKEYS

SS@ IF Ag="" THEN GO;u 288

S68 IF RBS<s"3F" THEN GOTO 168
278 FF COPE Ae=12S THEN GOTO 32
is

FEO LET Of=t8ti TO LEN Cs-1)}
QSOS PRINT RT PL,Pe;'"

SE@ LET Peoke-d

3220 GOTO i186

320 CF Cee" THEN GOTO 178

Explore the excellence of your ZX81 with a

ah
il

MEMOPBK 64k memory extension for $179.95

Give your diminishing memory more byte.

MEMOPAK 64K RAM $179.95
The Sinclair ZX81 has revolutionized
home computing. The MEMOPAK 64K
RAM extends the memory of ZX81 bya
further 56K to a full 64K. It is neither
switched nor paged and is Directly
Addressable. The unit is user trans-
parent and accepts such basic com-
mands as 10 DIM A (9000). !t plugs
directly into the back of ZX81 and does
not inhibit the use of the printer or other
add-on units. There is no need for an
additional power supply or leads.

Description of memory
0-8K ... Sinclair ROM
8-16K . . . This section of memory
switches in or out in 4K blocks to leave
space for memory mapping, holds its
contents during cassette loads, allows
communication between programs, and
can be used to run assembly language
routines.
16-32K ... This area can be used for
basic programs and assembly language
routines.
32-64K .. . 32K of RAM memory for
basic variables and large arrays. With
the MEMOPAK 64K extension the ZX81
is transformed into a powerful com-
puter, suitable for business, leisure and
educationai use, at a fraction of the cost
of comparable systems.

Memory Extention Specialists

Memotech Corporation
7550 West Yale Ave., Suite 200
Denver, Colorado 80227

Ph. (303) 986 = 1516

MEMOPAK16K RAM $59.95
With the addition of MEMOPAK 16K,
your ZX81 will have a full 16K of Di-
rectly Addressable RAM. It is neither
switched nor paged and enables you to
execute longer and more sophisticated
programs and to hold an extended data
base.

The 16K and 64K Memopaks come in
attractive, custom-designed and engi-
neered cases which fit snugly on to the
back of the ZX81 giving a firm connec-
tion.

Free service on your MEMOPAK
Within the first six months, should any-
thing go wrong with your MEMOPAK,
return it to us and we will repair or
replace it free of charge.

Try MEMOPAK with no obligation
You can use our MEMOPAK in your
home without obligation. After 10 days
if you are not completely satisfied,
simply return it for a full refund.

Coming soon.....
A complete range of ZX81 plug-in
peripherals:

MEMOTECH Hi-Res Graphics
MEMOTECH Digitising Tablets
RS232 Interface

Centronic Interface and
Software Drivers

All these products are designed to fit
“piggy-back” fashion on to each other
and use the ZX81 power supply.

Further information forthcoming.

| Yes! | would like to try the Memopak. | understand that if I’m not complete satisfied,
| can return it in 10 days for a full refund. Price t Qty Amount

| O) Check

Memopak 64k RAM $ 179.95 |
| O Visa Memopak 16k RAM |
| O Mc Shipping and Handling : |
| Act. No. [ et |
| Name |
| Street |
| City State Zip ; |
Me a a ea a al

HARDWARE REVIEW
Product: CAI/O Board and 40-column
Printer Model CAI/P40
From: CAI Instruments, 2559
Arbutus Ct., Midland, MI
48640, 517/835-6145.
Price: CAI/O board $79.95 alone,

$69.95 with any CAI peri-
pheral. Printer $119.95.

CAI Instruments has produced
and documented an easy-to-use,
relatively inexpensive printer
and interface for 8K ZX computers.
If you held off buying CAI's
Widget, you'll find the CAI/0O-
printer combination worth the wait.

As CAI's redesigned Widget,
the CAI/O board has serial and
parallel I/O ports plus CAI's prin-
ter interface and tape controller.
We only tested the board as it
works with the printer. As a side
note, the Widget has been stream-
lined internally to 7 chips and 3
EPROM sockets on a Single board.

By ZX standards the printer
is fairly large, about 10x7x2".
Hook-up could not have been easier.
The CAI/O board, needed to run the
printer, plugs onto the rear edge
connector of the computer. Another
connector accepts RAM, The prin-
ter plugs into the wall for power
and into the CAI/O board via ribbon
cable. The simple directions re-
quire no technical knowledge.

I had only two small problems:
After a few hour's operation, the
printer skipped characters in the
middle of the paper. Also, my
computer crashed with a program
loaded but not running crashed
after 2 hours. CAI replaced I/0
board and printer quickly and the
second units have worked perfectly
for over a week.

ZX81 keyboard printer commands
don't work with CAI's printer. You
use USR calls to routines in the
printer's internal software. For
example, to print out a program in
memory, type LET Z=USR 8195. Not
as convenient as LLIST, but just as

effective. Six USR calls operate
the printer in one of 3 modes:
print with variable (like LPRINT),
list program in memory (like LLIST)
and screen dump (like COPY). Each
of these 3 can be printed in either
regular or enhanced mode, which is
twice normal height. Check page 17
for an example of enhanced mode.

To print, the computer must be
in FAST. Internal software creates
3 error codes not used by Sinclair
to catch errors, so you won't crash
the computer by making a mistake.

You get 40 print columns,
which is wider than the ZX80/81's
screen display. CAI sells the 4.2"
thermal paper at $1.95/roll (but
any thermal paper that size works).

Unlike the Widget, this board
and printer don't eat up RAM. They
work with 16 & 64K RAMS (the 16K
pack needs no changes; for 64K cut
out the 8-16K block--DIP switches
set to 1-OFF 2-OFF 3-OFF 4-ON).

What I like about CAI's
printer: It operates quietly (un-
like Sinclair's). It can print in
large characters. It is available
now. And the documentation is easy
to follow and provides simple tests
of all functions.

What I don't like: Not being
able to use the keyboard printer
commands is moderately inconvenient
at first, although I quickly
memorized the most-used USR calls.
Because of the layout of the CAI/O
board's edge connectors, attaching
these units to 8K ZX80s is un-
wieldy. The design makes it tough
to plug in the power jack. And the
40-column output means you won't
get a program listing in screen
format, which I find useful for
proofreading. Also, the printer
puts an extra space after some
keywords like LET (see examples on
pp. 9 & 17), again messing up the
screen format.

But overall, these objections
are minor compared to the benefits
of these two units. I was very
pleased with the performance of my
CAI/O board and printer.--AZ

20

PROGRAM IMPROVEMENTS

Dave Tabor of Menlo Park, CA, sent
this version of Leo Morgan's sort
routine (Oct.81). It's two lines
Shorter and avoids Leo's lines 80
and 130 by using an inverted space,
which has a higher character code
than any standard word. Add back
prompts as in Leo's program for a
user-friendly routine.

i@ INPUT wn

iS DIM Retin, 242
#0 FOR F=1 TOA N
BS INFuY Aeer
3S@ NEXT §F

4@ FOR Yei To N
45 LET Feil

SS FoR M=2 FON
SS IF AStK) eASth) THEN LET Fst
6&@ NEXT X

S5 PRINT ASIF:
7O LET AS TF: ="Ee
7S NEXT YY

CLASSIFIED ADS

Reach thousands of ZX80/81 owners!
Send your ad, typed 35 char/line,
with check to arrive by the 15th of
any month for the next month's
issue. Ads arriving after the 15th
appear in the issue following the
next unless you. request its return,
Ads are $9 per line and must be
resubmitted for each month. No
phone orders or credit cards. We
take no responsibility for adver-
tisers. SYNTAX Classified Ads, RD
2 Box 457, Harvard, MA 01451.

DUNGEON OF DOOM and INTERGALACTIC
TRADER.Two high-quality games that
run on 16k.DofD is an action packed
Adventure.IT is a game of cosmic
Ssurvival.Send $7.95 to M.Brletic
1072 N.Sunset,Reedley,CA 93654 ***

For Sale; Sinclair 16K Ram Pack
$50.00 W.B. Emery 2000 Burton Dr.
Austin, Tx. 78741 ph.

(512) 445-0423

FIFTY NIFTY PROGRAMS FOR YOUR ZX81
Book has 50 Top Quality 1K programs
w/instructions+comments. Full of
GAMES/GRAPHICS/FUNSTUFF. ONLY $7.95
LEE CARTER Bx 246 Harrison ME 04040

21

RRKEKEKKEKRKEKRKEEREKREREKRKRREEREREREREERERER

A challenging and highly addictive
new video game--LETTER RAIDERS, de-
veloped by NON-TRIVIAL SOLUTIONS.
The strategy is to capture each
letter of the alphabet on a 24 x 32
grid without recrossing your path,
Also available--LIFE, a simulation
of biological systems, with high
speed 48 x 64 graphics palette.
Both well-documented games are
written in machine language for the
ZX81 with 16K. Order by mail or
phone at $9.95 each from N-TS, P.O.
Box 2941, Amarillo, TX 79105, 806/
376-5723. Check, Visa, MC welcome.
Watch for exciting new developments
coming soon from NON-TRIVIAL

SOLUTIONS!
RK KK KERR KRER EERE KR KEKE RREREREREREERE

***XDISCOUNT ZX-81 (1K) PROGRAMS***
(8)Programs on each 8.00per tape.
Tape(l)games:Lunar Lander and more.
Tape(2)Business:Salary,Markup% etc.
Tape(3)Investment:InterestComp.etc.
ROMAN SOFTWARE 788 MERCURY CIRCLE.
LITTLETON COLO. 80124

ADVANCED SOFTWARE FOR 16K ZX8l's!!!
ZX-FORTH, ZX-CALC (Spreadsheet), ZX-
FILE, ZX-BUDGET, ZX-PLAN(Personal
Calendar), ZX-INVENTORY. $20 EA. OR
3 for $50 or all for $100. Softek,
Box 4232, Santa Fe, NM 87502-4232,

FREE business and personal software
- hardware CATALOG for ZX80/81 and
M.Ace. Send a SASE to: M.C.Hoffman
P.O. Box 117, Oakland, N.J. 07436

2K Memory Hm6116 Static Ram Chip
12.50 &1.00 shipping 28 Pin Solder
Tail Socket .95 & .50 Shipping
Send Check or MO to: M. S. P.

PO Box 187 New Windsor,Md. 21776

Direct from the author.-Air Mail
Understanding your ZX81 Rom
Sinclair Rom disassembly partA $15
Sinclair Rom disassembly partB $17
U.S. Personal cheques/money order

Accepted.
Ian Logan, 24, Nurses Lane,
Skellingthorpe, Lincoln LN6 OTT, UK

KKK KITS ** KITS ** KITS ****

LIGHT PEN: draw and erase right

on your TV screen with this magic

wand. Eliminates PRINT & PLOT !

SUPER GRAPHICS: Control every

DOT on your screen. Transfer any

photo image in minutes !

INTERNAL 6K MEMORY: Upgrade to 4

or 6K as you need it.Convenient!

CONTROL MODULE: 8 inputs-8 outputs

aad your own relays for ROBOTICS!
Assembled 69.95 KIT 49.95

ANY PC BOARD 15.00 Easy software.

Write ZODEX, EAST HILL, Oakham,MA.
KKKKKKKKEKEKEKK 0106Q RRRKKKRKKKKK

Tired of Playing? BUDGET PROGRAM
for 8kROM 16kRAM on cassette.GET
TO WORK! $10 To: BAXGRAFAX 322

Ladera#1ll Santa Barbara,CA 93101

Coming Soon!-"ZX81 Monopoly" (c)
16K RAM-up to 6 players-imported
from the UK. Spanish Board Version.
Savage Sortware P.O.Box 892

New Smyrna Beach, Florida 32069

BUFFERED BUSS/DEVELOPMENT BOARD for
ZX80/81: $34=BARE. BOARD+ZX conectr+
Manual. $64=KIT. W/plans: Ram&port.
Hundreds sold;no complaints. See ad
in Sync. Prices to rise in Aug. UHF
MODULATOR $15. Connectors $6. Send
stamp for info,or order now. Prompt
ship. COMPUTER CONTINUUM, 301-16 Av
San Francisco CA 94118. (415) 7526294

COMPUSETTE is a C-10 Cassette which
is especially designed for micro-
computer application by TAPEMASTERS
25°f0r S20, 00 100 for $70.00
VISA MASTERCARD C.0.D.
TX 214-349-0081**OTHER 800-527-1227
10% DISCOUNT for Check with Order
P. O. Box 38651*Dallas, Texas 75238
FREIGHT PREPAID*DEFECTIVES REPLACED

LOWEST PRICE VIC 20 COMPUTER: $ 245
KM 1200 VIDEO MONITOR green 20MHZ

6 month unconditional warranty $ 75
For ZX 81 free adaptor & instructio
n.call collect for VIC & Commodore
oeripherials. checks or money order
General Technology. 15 Exeter st
Providence, R.T. 02906 401 274 8829

SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS$
$ZX80/81 16K RAM Plug in and run.$
$ New product with super connectors
$ Fully tested w/90 day warranty. $
$ ONLY $45.95 plus $4 shipping. $
$(Ca,add 6%Tx) Send check or MO to$
SAPROPOS TECHNOLOGY 350 Lantana$
$ Suite 821 Camarillo,Ca. 93010 §$
$ VISA or MC phone 805/482-3604 $
SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS$S$s

Coming Soon! "Trader Jack"

16K RAM - Imported from the U.K.
Fantastic - Beats Rubic's Cube!
Polynesian Trader - Inter Islands.
Hazards, Profits, Losses, Storms.
Savage Software PO Box 892

New Smyrna Beach, Florida 32069

ZX81-A DAY IN LAS VAGAS on cassette
with HORSERACING STREET-CRAPS BINGO
BLACKJACK RED-DOG ROULETTE BANDIT.

Quality+Action+Mult-Player Options

equals a lot of fun - ONLY $19.95.
HI-TECH(a),47 Greenwood Cr, REGINA

SASK, CANADA, S4X 1G5

TURN ANY TV INTO A 7 FOOT SCREEN TV
All games and TV more fun!EZ Kit$20
HENSLEY, BOX 334, ASHEBORO NC 17203

GRAPHICS pgms that make screen a
playground. Sketch, Maze, Mandala,
Round 'n Round. Fun for all. 16K
ZX-81. Cassette. $15.00 ppd. SCREEN-
MAKERS, 351 Badger, Guffey, CO80820

From the SYNTAX bookshelf: NEW!
Laminated Microprocessor Instant
Reference Cards for 280, 6502,
8080A & 8085A, 8048&relatives, and
programmers' Algorithms ref. card,
$5.95 each. Zilog Z80A CPU Tech
Manual, $7.88; Assembly Lang. Pro-
gramming Manual, $15.75. Crash
Course in Microcomputers, $19.
Pocketbook w/8K supplement SALE
$10.95, back issues SYNTAX $4 each.
All prices include shipping.
SYNTAX, RD 2 Box 457, Harvard, MA
01451, 617/456-3661.

ZX80

EXPAND THE SINCLAIR WITHOUT LIMIT
Interface to STD-Bus $79 A&T $29 BB
AERCO Box 18093 Austin, TX 78760

22

SPECIAL3 PROGRAMSZX81SEND$1+SASE
to PO Box 3073 San Jose,CA 95156

TEACHERS/PARENTS--4 pgms on tape
for teaching pre-schoolers, Spec.
Educ. students readiness concepts
more/less, same/different, no. rec-
Oognition, counting. Reports statis-

tics for your evaluations, IEP,
etc. Fun ZX-81 graphics. Specify
1K or 16K version. $20 PPd. SCREEN-

MAKERS, 351 Badger, Guffey, CO80820

OUR POLICY ON CONTRIBUTED MATERIAL

SYNTAX invites you to express opinions related to any Sinclair computer or
peripheral, or the newsletter. We will print, as space allows, letters discussing items
of general interest. Of course, we reserve the right to edit letters to a suitable length
and to refuse publication of any material.

We welcome program listings for all levels of expertise and written in either
Sinclair BASIC or Z80 machine code. Programs can be for any fun or useful
purpose. We will test run each one before publishing it, but we will not debug
programs; please send only workable listings. Programs submitted on cassette can be
tested more quickly and with less chance of error.

In return for your listing, we will pay you a token fee of $2.00 per program we
use. This payment gives us the nonexclusive right to use that program in any form,
world-wide. This means you can still use it, sell it, or give it away, and so can we.

We will consider submissions of news and hardware or software reviews. Please
keep articles short (350-400 words). Again, we reserve the right to edit accepted
articles to a suitable length. We will pay 7 cents per 6 characters, including spaces
and punctuation, for accepted articles.

When you send in programs for possible publication in SYNTAX, please
include the following information:

¢ How to operate the program, including what to input if it does not contain

prompts.

¢ Whether you can run the program over again and how.

¢ How to exit the program.

¢ The Syntactic Sum (program published in Feb. 81 and Jun. 81; send SASE

for a free copy).

© What RAM size program requires.

© What ROM program uses.

We pay for this explanatory text at the same rate as for articles in addition to
payment for the program itself. ;

If you want us to return your original program listing or article, please include
a self-addressed, stamped envelope. Otherwise, we cannot return submitted material.

RRKEKEKKEKKEKKEKKEKKEKREKRRRRRRKRKEKKEKKKKKKEE

*FIND OUT WHAT THE SINCLAIR CAN DO*
*The new TS1000/2X81/ZX80/Microace*
*SOURCEBOOK lists 100s of programs*
*books, and accessories from over *
*60 manufacturers.ONLY $4.95+$1.25*
*p&h. Send check or MO to Atlantic*

*Computer,POB 936 Norfolk,VA 23501*
KEEKRKEKREKRREKRREKRKRRREKRKEKEEKEKKEERRKRKERKEREEE

** SALE ZX-81 CONNECTOR $4.75,5/$20
2K RAM-update to TS1000 RAM,S16.95
0-10 Port I/O ,D/A,A/D, 16-48 K RAM
SASE gets details,add 50¢%/item P&H.
POWERTRONIX 25E23 BAYONNE,NJ.07002

PUT THAT ZX81 TO WORK!! Low cost-

high performace software, explana-
tions that enlighten. Free catalog.
Tom Woods Box 64 Jefferson,NH 03583

TEXT EDITOR/WP, Other. D.O'Connell
1219W.Russell,San Antonio TX 78201

ZX81 TEE SHIRT-LARGE 3" RED LETTERS
on blue quality shirt.$l0.ea. PPD

(S) (M) (L) (XL) .SHEEPSCOT PRODUCTS
TOWNHOUSE RD. N.WHITEFIELD,ME 04353

Load Everytime with LED loader. Kit

$6+ $1 S&H. Play Gumshoe 8K/2K $2.50
+.35 S&H. R.H. Enterprises, 1408 N.

4th Ave., Newton, Ia.-50208

SE ESSE ESS SSE ST SSE ESS SSS ST ESS TS EET SS EES 2 SS GES SSIS OCS

SYNTAX ZX80 is published

monthly by a wholly-owned
subsidiary of The Harvard Group.

Syntax ZX80, Inc.

RD 2, Box 457, Harvard, MA 01451.
Telephone 617/456-3661.

YES! Please send me 12 issues of SYNTAX for $29.

L] My check for $29 is enclosed.
Make checks payable to:
SYNTAX ZX80, INC.

(] Please charge my 1} MasterCard

LJ VISA CJ] Carte Blanche account

account number

(} Diner’s Club L! American Express

rights reserved. Photocopying

ZX819S

|
|
|
i
t
I
|
!

12 issues, $29. Single issue, $4. exp. dale bank number (Mc only)
| Signature

Publisher: Kirtland H. Olson ' ;
N Titl
Editor: Ann L. Zevnik aes si

Levees bane

Printed by Joseph E. Marhefka, Jr. ; ee a

Clinton Offset Printers ! Address
Clinton, MA 01510 ' City State Zip

|

©) Syntax ZX80, Inc., 1981. All | Day Phone _( ) Evening Phone ( )
|
i]

prohibited. ISSN 0273-2696

23

I own a L] Sinclair ZX80

|_J Sinclair ZX81 Telephone orders call

617-456-3661

T have a 44 key tactile feel key-
board that plugs into ZX81 or TIME
/SINCLAIR 1000 incldg. all graphics

(4keys=Edit, Delete, ", Functns)
Price: $70(Mass. Res. add %5 sales

tax) Shpg. & Hndlg.=$4. Send Chk.
or M.O,. tok,%,KEY; Suite 75; 711
Southern Artery;Quincy, Ma. 02169

Loading Problems? -- Our cassette
interface is the answer. Complete
system, 29.95. Phoenix Engineering
Systems, 4240 Lakeshore Rd., Deck-
erville, HMI. 48427

--- FANTASTIC SPACE WAR GAME ! ----
X-81 SPACE RAIDERS for 2X-81 w/ 16K
ML graphic and math routines create
fast, exciting, accurate simulation
of space navigation and battle.
$19.95 for cassette, manual, and
keyboard overlay. NIRAD ELECTRONICS
959 East 460 So., Provo, UT 84601

RKEKKKKKKEKTHR FUNWARE CO. RRRKAKKKKK
1.LAND THE SPACE SHUTTLE 2.LAND/AIR
BATTLE 3.SPACE BATTLE 4.HUNTMAN*ALL
ZX-81/16KRAM ON QUALITY C-20 TAPES.
EACH GAME $4.95 OR ALL FOUR $16.95.
7119 Santa Fe Av. Dallas, Tx. 75223

ZX81/1K listings: Bomb-destroy en-
emy. Guess-guess No. using clues $1
+SASE to Mark Neirick, 9105 Hol-
lyberry, Des Plaines, IL 60016

THE
HARVARD
GROUP

Bolton Road, Harvard, Mass. 01451

SYNTAX

24

"TSLE" A war game for 8K/1K
Soldiers under your command must se
cure foothold on enemy-held island,
then move across it and take enemy
stronghold.Not a simple prog. List-
ing w/map,game instrs, and syntac~
tic sum for $2 CASH ONLY
TIMESTOPPER, 31 East Mockingbird Ln
Lawrenceville, GA 30245

LOW LOW LOW LOW LOW LOW LOW LOW LOW
PRICES!
Biorhythms 8K ROM/1K&up........1.00
Graphics Billboard 8/lup.......1.00
Horse Rate 8/7 1UDsiassi eines de
SPINNER TM(like Rubik's) 8/16...2.00
Improved ZX81 PAUSE.......-++---1.00
Linear Regression 8/lup........2.00
SASE gets you our GOODIES CATALOG
ORDER gets you !!FREE!! PROGRAM
EZRA GROUP II
EZRA GROUP II
POB 5222 San Diego,California 92105

ADVENTURE-DRY GULCH. 16K Search for
treasure in a ghost town. Written
in BASIC, listable, can be saved in
progress. $10 (NY add tax) UPSTATE
LABS. 27 ELVIRA ROCHESTER, NY 14606

2 LISTINGS $1 BLACKJACK+SLOTMACHINE
just like Las Vegas,Atgraphics 16K

MONEY BACK GUARANTEE Send $1 + SASE
to: FLORIDA CREATIONS ,Dept S,PO Box
16422 Jacksonville,FL 32216 Thanks.

U.S Postage
PAID

First Class

Permit No.
451

Harvard, MA

8